The invention relates to testing of memories and more particularly to a device for locating faults in a memory such as a random access memory.
The random access memory (RAM) is widely used for its capability of permitting arbitrary read and write at any address. To insure that a memory is able to properly store and maintain data, various diagnostic testing equipment has been introduced to check the function and operation of the memory.
U.S. Pat. No. 3,940,601 to Henry et al shows a prior art test device for locating faults in a working storage. The device includes an auxiliary storage which holds a sequence of test words and for cyclically writing the test words into the working storage reading the test words out of the working storage. A bit for bit word comparator compares the words read out of the working storage with the words read into the working storage and detects bits of the words which do not match in order to identify defective components. First and second registers record the row and the column to which the defective component belongs.
U.S. Pat. No. 4,300,234 to Maruyama et al discloses another test device including an address pattern generator for testing semiconductor memories such as a random access memory.
The present invention was designed and built especially to test memory cards of the general purpose signal processor unit of the AN/FPS-115 radar system. The need for the invention became apparent when it was found that implementation of available diagnostic tests failed to detect whether every card of the general purpose signal processor was functioning properly. In certain situations the diagnostic tests were unable to identify a memory failure. After careful evaluation, it was determined that the radar system operated at a much higher frequency than the frequency in which the memories were being tested, and as a result memory failures were most likely related to timing errors generated within the memory itself. Prior to the invention, diagnostic tests were unable to adequately detect and locate all malfunctions in memory modules of the general purpose signal processor, and as a result entire memory modules had to be replaced, and the faulty modules returned for costly depot maintenance.
An object of the present invention is to provide test apparatus for testing a random access memory at its normal operating frequency.
Another object of the invention is to provide a test apparatus capable of isolating failures in large memory modules at a high rate of speed.
Still another object of the invention is to provide a portable self-contained minicomputer that requires no software and which generates a series of test words for testing a memory.